The invention concerns a multilayer body having a transparent first layer in which a multiplicity of microlenses is shaped, and a second layer which is arranged beneath the first layer in a fixed position relative to the first layer and which has a multiplicity of microscopic structures, and a process for the production of such a multilayer body.
Multilayer bodies with microlenses and microimages arranged beneath the microlenses are used in different ways as security elements for security documents such as for example banknotes or credit cards.
Thus on the one hand security elements are known, in which there is arranged a two-dimensional array of spherical microlenses above a two-dimensional array of identical repetitive microimages. Such an arrangement is described for example in U.S. Pat. No. 5,712,731. The security element has a multiplicity of identical spherical microlenses arranged in accordance with a regular two-dimensional microlens grid. The security element further has a multiplicity of identical printed microimages arranged in accordance with a regular two-dimensional microimage grid. The period of the microimage grid and the microlens grid is identical. The spherical microlenses arranged in the microlens grid produce a reproduction of the microimages, which is enlarged point-wise, so that overall an enlarged representation of the microimage becomes visible to the viewer. As the pixel, respectively represented by the microlenses, of the respective microimage changes in dependence on the viewing angle, that affords an optically variable impression of the enlarged representation of the microimage.
Arrangements of microimages and microlenses are also known, in which two or more different microimages which are visible in dependence on the viewing angle are associated with a microlens. Thus DE 103 58 784 A1 describes for example a data carrier in which different items of information which include for example a serial number of the banknote are written in by means of a laser beam at different directions. A recording layer of the data carrier is locally blackened by the action of the laser beam so that, for each of the items of information which are written in at different directions an associated microimage is written in, beneath each of the lenses. Thus, provided beneath each of the microlenses are a plurality of microimages which become visible at different viewing angles. In that case the respective microimages associated with the same item of information respectively contain only a part of the items of information which are composed of the representation of the individual microimages. By virtue of the high information density (a plurality of microimages per microlens) and the high demands in terms of register accuracy of the association between microimages/microlenses, it is necessary with that process to use microlenses of relatively large dimensions and to effect recording of the microimages in the recording layer only after the application of the microlens array to the recording layer, individually for each security document, resulting in disadvantages in regard to production costs.